1. Field of the Invention
The present invention concerns a machine for the production of ice-cream, of the type comprising a pressurized gas refrigeration circuit.
2. Description of the Prior Art
Machines are known for the production of espresso ice-cream, consisting of a vat for the storage of the mixture to be frozen in liquid form, a mixing and whipping cylinder for said mixture and a manually-operated tap through which the mixture is dispensed.
More precisely, the mixture is fed either by gravity or pump from the storage vat to the mixing and whipping cylinder where it undergoes a further refrigeration and is mixed and forced through the tap-dispenser by a mixer-web.
Both the storage vat and the mixing and whipping cylinder are cooled by coils connected to the refrigeration circuit and in intimate thermal exchange relationship with the exterior surfaces of the same vat and cylinder.
At predetermined times the mixture in the vat and cylinder must be pasteurized to prevent the deterioration of the mixture through the build-up of bacteria. To achieve this, the vat and cylinder must be heated and maintained for a predetermined time at a temperature sufficiently high to kill germs.
This has been achieved in espresso ice-cream machines known up to now, by having both the vat and the mixing and whipping cylinder in thermal exchange relationship with electrical resistance heaters which supply the heat necessary to raise and maintain the temperature at a level sufficiently high to destroy germs.
Such electrical resistance heaters, besides complicating the construction of the machine, use significant quantities of electricity, which raises the operating costs of the machine considerably.